I am a first time home buyer and need to locate my clean out. I am on a sewer system. What do I need to look for and how far from the house would it be?

If you have one outdoors, it should be within a few feet of the foundation where the building sewer exits the building -- But not all homes have outside clean outs.

Does the home have a crawlspace or a basement?

Clean outs are usually (but not always) located close to where the building drain exits the building.

If you have a basement look on the street side near the floor for a clean out.
If you have a slab house SPC, (Standard Plumbing Code) mandates that we install a 4" cleanout not over 18 inches from the foundation and bring it up to grade.
However, sometimes over time grass and dirt will cover the cleanout up. We then take a pointed rod called a probe, (a long screwdriver will do) and go hunting for it by jabing it into the ground until we hit it. As a rule it can be found on the street side of the house but we have been known to exit out the sides. Good luck, Tom